The invention relates to an optical movement sensor for the detection of a human body.
In computerized tomography, particularly nuclear spin tomography, intestinal, swallowing and muscular movements of a human body as well as movements originating from respiratory or heart activities produce so-called artefacts (i.e. shadows on the images of cross-sections lying at right angles to the body axis). The artefacts can falsify the examination result. To obtain perfect sectional images it is necessary therefore to clearly detect deformations of a human body under examination and take these into account in the production of the sectional images.
German Pat. No. 8012386 (corresponding to U.S. Pat. No. 4,559,953) describes a capsule-shaped sensor for the detection of deformations of a human body. The sensor contains a hollow space sealed off with an elastic membrane and filled with air. The hollow space has an aperture which is connected via a hose to a volume transducer.
The sensor is fixed by adhesive strips to the human body under examination in such a way that the elastic membrane lies on the body and is deflected with deformations of the body. The change which this brings about in the volume of the hollow space is detected and indicated by the volume transducer.
Because the membrane has a very thin wall, air in the sensor is heated up. The heated air expands causing the measured results supplied by the volume transducer to exhibit a measuring error which depends the temperature of the capsule-shaped sensor. Thus, the measured results depend on both the shape of the body being examined and on the temperature of the sensor. The measured results cannot therefore unequivocally indicate the state of deformation of the body.